Solution

Click "Add" to add files to be merged one by one, or choose "File\Add a Directory (Include sub folders)" to add a folder of files directly, even you can use Drag and Drop to add files (If you want to merge Office files please ensure you have installed A-PDF conversion programs)

Choose the file then right click choose "Merge Method" and select "Mix alternate pages" input you desired alternate page number, you can also set Actions as merge sequence, and Options in "Tools" such as Properties, Security, Bookmark, Page Number etc.

Click "Merge", choose a folder and input a File name for outputting to complete the operation

This web tutorial will give you an overview of the procedure how easy to use this product!